I have a 1971 20 hp Merc with electric choke and mine is a solenoid that closes the choke when pressed. So in my case I hold the choke button and crank the engine, when it starts I release the button, in cold weather you might have to hold it a little longer.
Mine also got to where it wasn't always working and I had to take the button apart and clean the contacts.
You can see if yours is like mine, take the cowling off & look at the carb throat when you press the button you should see the coke plate cover the opening. This helped me understand how mine worked.